1. Field of the Invention
The invention generally relates to an adjustable lens assembly applicable to a lens of a camera, camcorder, surveillance system or the like, and more particularly relates to an adjustable lens assembly in which a lead screw mechanism is used to move the lens for the purpose of focusing or zooming.
2. Related Art
In a lens module, in order to minimize the size, a lead screw mechanism is usually used to move the lens for focusing or zooming. When using the screw mechanism, the gear shaft and the guiding elements should be well fabricated and mounted in parallel, otherwise smooth movement cannot be obtained. Any unsuitable tolerance in manufacturing or assembly of the gear shaft or the guiding elements will cause bias in the elements. In order to solve this problem, a prior method is to lessen the bias by improving the precision of fabrication and assembly of the elements. Another method is to increase the backlash between the gear shaft and the meshed nut for absorbing the clearance or bias. Though the two prior methods can solve the problem, the first one increases the tooling cost of the elements and the time cost of assembly, while the second one increases the backlash that will cause defects of imprecision movement, vibration and noise.
In a transmission mechanism, two parallel axes C1 and C4 located in two parallel planes P1 and P2, as shown in FIG. 1, have to be kept in parallel theoretically. However, due to tolerance in manufacture and assembly, the distance between the two axes cannot be kept constant along the direction of the axes; for example the distances d1 and d2 do not remain the same between the axis C2 and the axis C1. Technically, the difference, called the xe2x80x9cbias,xe2x80x9d includes two conditions. One is inclination between two axes, for example C1 and C2, located on a co-plane. The other is skew between two axes, for example C1 and C3, located on two non-parallel planes. Bias will cause the transmission mechanism to become clogged, run awkwardly, noisily and waste power. Since the bias, and especially the skew, occurs frequently in the fabrication and assembly of a lens assembly, it is an important issue for the industry that requires an effective solution.
Some prior arts for solving the aforesaid problem are disclosed in U.S. Pat. Nos. 5,150,260 and 5,815,325. As shown in FIG. 2, the prior art uses a rack and a screw for transmission. The rack has an opening to allow inclination of the screw in the parallel plane of the opening. However, when the axis of the screw has a skew bias with the axis of the guide, an angular moment will be generated when the screw drives the rack. The opening gives only one dimension of freedom that is not enough for preventing the lens assembly from being clogged or running awkwardly.
U.S. Pat. No. 5,150,260 provides an optical apparatus with a moving member that has a gear portion meshing with a gear shaft that is movable in the direction of the optical axis and is driven by the rotation of the gear shaft to thereby move the lens holding member in the direction of the optical axis. The moving member is supported in a direction substantially orthogonal to the axial direction of said gear shaft. U.S. Pat. No. 5,815,325 discloses a lens assembly that comprises a lens barrel assembly for supporting a lens barrel, one or more guide members for guiding the movement of the lens barrel assembly in the direction of an optical axis, a gear shaft that is rotated by a primary mover, and a drive linkage for coupling the lens barrel assembly with the gear shaft. The drive linkage has a drive nut portion meshing with the gear shaft over a threaded partial circumference section thereof and movable in the direction of the optical axis by the rotation of the gear. The aforesaid two patents try to solve the skew bias by adjustments of two degrees (a linear movement and a rotation), but the bias doesn""t include the skew of the axis in two different planes.
As described above, some conventional lead screw driving mechanisms for lens assemblies provide only one direction of adjustment, as illustrated in FIG. 2. Though some other mechanisms, as disclosed in U.S. Pat. Nos. 5,150,260 and 5,815,325, further provide means for adjusting rotational bias, the rotational adjustment is still limited in a plane passing through the optical axis. In other words, they do not solve the common problem of three-dimensional bias of the driving shaft to the optical axis. Another problem is the transmission method of the rack with an opening that slips easily.
The object of the invention is therefore to provide an adjustable lens assembly having a transmission mechanism with multiple degrees of freedom that can solve the problem of skew bias of the driving shaft to the optical axis.
To achieve the aforesaid object, an adjustable lens assembly according to the invention includes a lens barrel for carrying the lens, a guiding member having a shaft axis parallel to the optical axis of the lens barrel for guiding the direction of movement of the lens barrel, a gear shaft driven by a motor, a driving member meshing with the gear shaft, and a connection mechanism connecting the lens barrel and the driving member. The connection mechanism is capable of adjusting itself with multiple degrees of freedom so that if there is three-dimensional skew bias between the gear shaft and the optical axis or the guiding member, the lens barrel can be driven smoothly.
Further scope of applicability of the invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.